Integrated circuit devices are typically fabricated in what is commonly referred to as a clean room environment. As the term implies, a clean room environment can be essentially free of particles that can affect the yield of the integrated circuits produced in the clean room. In particular, substances, either created during the manufacturing process itself or introduced to the clean room via external air supplied to the clean room, can contaminate the integrated circuits produced by the clean room thereby leading to their premature failure.
The types of devices fabricated in the clean room can dictate the degree of filtering of external air provided to the clean room. For example, studies have shown that in order to reliably produce 256 MB DRAMs having a design rule of 0.25 μm, particles having a size greater than 0.25 μm should be removed or filtered from the clean room. In addition, the temperature, humidity, and pressure of the air in the clean room may be controlled. Other types of environmental factors, such as illumination, noise, and vibration, may also be controlled.
In order to provide the filtering discussed above, air is provided to the clean room through an air conditioning apparatus having filter units that can filter external air (i.e., air obtained from an external environment) to the clean room. In particular, in some conventional approaches, fresh air produced by the air conditioner is introduced below the floor of the clean room which is then circulated above the ceiling of the clean room and into the clean room.
As the concentration of fine particles contained in the external air is increased, it may be difficult for a conventional air conditioner to filter the air to the level needed by the clean room which can increase contamination in the clean room resulting in a decrease in the yield of integrated circuits manufactured in the clean room. For example, a phenomenon referred to as “yellow sand dust” (or “dust”) can dramatically affect the yield of integrated circuits produced in a clean room. The yellow sand dust phenomenon can be characterized as when the external air includes an abnormally high level of sulfuric oxide, nitric oxide, and/or silicon. The yellow sand dust phenomenon can occur at particular times of the year and in particular geographic locations. For example, measurements in the area of Seoul, Republic of Korea in the year 2001, showed that density of dust in the air during the occurrence of the yellow sand dust phenomenon was about 7 to 14 times greater than the density at other times of the same year in the same location. In particular, the density of the dust was measured to be in a range between about 473 μg/m3 and about 999 μg/m3 during 2001 in Seoul. Furthermore, ozone, SO2 and/or NOx contained in the external air during the summer months can in turn be introduced into the clean room if proper filtering is not performed.
FIG. 1 is a greatly enlarged schematic view that illustrates a particle 10 lodged on a pattern 20 of an integrated circuit in a clean room. The particle 10 can cause the integrated circuit to be inoperative or to function improperly. The particle 10 can be about 0.05 μm in diameter and have a circular or annular ring shape.
FIG. 2 is a graph that illustrates measured compositions of the particle 10 shown in FIG. 1. In particular, an EDS (Energy Dispersive X-ray Spectrometer) shows that the particle 10 can include significant amounts of silicon and oxygen which are present in the composition of the dust produced during the yellow sand dust phenomenon. As shown in FIG. 2, many of the particles shown in the EDS have a size less than 0.05 μm.
It is known to use an air conditioner including an HEPA (high efficiency particulate air filter) and a chemical filter to filter air provided to a clean room. U.S. Pat. No. 5,890,367 to You et al. entitled Air Conditioning System for Semiconductor Clean Room Including a Chemical Filter Downstream of a Humidifier discusses the removal of chemical impurities from the air provided by the air conditioner, such as phosphoric acid generated by the process of manufacturing the integrated circuits, using a chemical filter located between the air conditioner, having a humidifier, and an ULPA (ultra low penetration air) filter.